Valve Drive Assembly for an Internal Combustion Engine

ABSTRACT

The invention relates to a valve drive assembly for an internal combustion engine. The aim of the invention is to improve the assembly in such a manner that a stationary cam can be reliably connected to a cam that is rotatably mounted on the camshaft and to avoid malfunctions. For this purpose, a groove-type guide is arranged in the area of the base circle of the cam which is rotatably mounted on the camshaft. A pilot locking plunger is mounted in a blind bore of the base circle of the cam that is connected to the camshaft so as to rotate with it. The plunger can be displaced in a controlled manner and can be engaged with the guide disengaged therefrom. The groove-type guide in which the pilot locking plunger engages extends in the base circle of the rotatably mounted cam by approximately 180°.

The invention relates to a valve drive assembly for internal combustionengines with the features indicated in the preamble of claim 1.

From DE 42 28 796 A1, a variable valve drive for internal combustionengines is already known, wherein the gas-exchange valve is operatedwith different cam contours for adjustment of the valve lift and/or ofthe valve control times. For this purpose, one cam is mounted rotatablyon the camshaft, and the other cam is mounted rigidly on the camshaft.In the full-load range of the internal combustion engine, an electroniccontroller injects pressurized oil into a hydraulic chamber of the fixedcam, by way of an isolating valve, and thus displaces correspondingplungers, whereby the fixed cam is coupled, by means of shape fit, withthe cam mounted rotatably on the camshaft, by engaging the plunger intoa bore disposed in the cam region of the rotatably mounted cam. The camcoupled by means of shape fit actuates the respective gas-exchangevalves with relatively large lift, by way of a tappet. In thepartial-load range, with the oil pressure disconnected, the two camscoupled with one another become separated. The fixed cam with small liftactuates the tappet, while the cam mounted rotatably on the camshaft isuncoupled and the camshaft rotates freely in this cam. To ensure thatthe displaceable plunger can engage into the corresponding bore in therotatable cam during coupling of the two cams, an entry ramp is disposedin front of the bore in the cam region.

A disadvantage of this solution is the small range for the interlockingplunger to engage into the bore of the rotatably mounted cam, duringconnection of the two cams by means of shape fit. In this connection,malfunctions cannot be precluded, especially in the case of torques thatalternate in their direction of rotation.

The invention is based on the task of creating a valve drive assemblyfor an internal combustion engine of the type in question, with whichsecure connection of a fixed cam with a cam mounted rotatably on thecamshaft is achieved, and with which malfunctions are avoided.

This task is accomplished, according to the invention, by means of thecharacterizing features of claim 1.

According to the invention, in a valve drive for an internal combustionengine, with at least two cams disposed on a camshaft and provided withdifferent profiles, which cams selectively actuate at least onegas-exchange valve, and wherein one cam is connected to the camshaft soas to rotate with it, and the other cam is mounted rotatably on thecamshaft and can be connected, by means of shape fit, to the camdisposed on the camshaft so as to rotate with it, by way of acontrollable locking plunger, a groove-like guide is disposed in theregion of the base circle of the cam mounted rotatably on the camshaft,with which guide a pilot locking plunger, which is mounted so as to becontrollably displaced in a blind-hole bore of the base circle of thecam connected to the camshaft so as to rotate with it, can be engagedand from which guide it can be disengaged. The groove-like guide, intowhich the pilot locking plunger can engage, extends by approximately180° in the base circle of the rotatably mounted cam.

The advantage of the solution according to the invention consists in thefact that, during the operation of interlocking of the two cams with oneanother, a range of approximately 180° is available, in which a pilotlocking plunger can be inserted without problems. In this way, faultyswitching operations are very largely precluded. After insertion of thepilot locking plunger, the rotatable cam is carried along by the pilotlocking plunger, so that, by virtue of the equal speeds of the two cams,the main locking plunger can then engage into the corresponding bore inthe rotatably mounted cam, without problems, and ensures torquetransmission during running operations that alternate in theirdirection.

The invention will be described in greater detail hereinafter, on thebasis of exemplary embodiments, with reference to drawings. Theassociated drawings show:

FIG. 1: a schematic diagram of the valve drive according to theinvention, in section, with interlocked cams,

FIG. 2: a section A-A according to FIG. 1,

FIG. 3: the main locking plunger as a detail x-x according to FIG. 1,but in the de-interlocked position, and

FIG. 4: the pilot locking plunger offset by 90°, as a detail y-yaccording to FIG. 1, but in de-interlocked position.

FIG. 1 illustrates a longitudinal section of the valve drive accordingto the invention, wherein a fixed cam 2 and a cam 3 mounted rotatably onthe camshaft 1 are disposed next to one another on a camshaft 1. Bothcams 2 and 3 have the same base-circle diameter 14 and 15. The rotatablymounted cam 3 possesses a larger profile height than the cam 2, formaximum valve lift during full-load operation of the internal combustionengine. The cam 2 is designed for a small lift or for zero lift, forpartial-load operation of the internal combustion engine.

When a cam 3 is de-interlocked from the cam 2, only the cam 2 acts on aroller-type cam follower or tappet, not shown, which actuates one ormore gas-exchange valves of a cylinder of the internal combustionengine. In this condition, the camshaft 1 rotates freely in the cam 3.When the cams are interlocked, only the cam 3 acts on a roller-type camfollower or tappet, not shown, which actuates one or more gas-exchangevalves of a cylinder of the internal combustion engine. By virtue of thesmaller profile height of the cam 2, it does not become engaged with theroller type cam follower or tappet when it is in the coupled condition.

According to the invention, interlocking of the cam 2 disposed rigidlyon the camshaft 1 with the cam 3 mounted rotatably on the camshaft 1takes place by means of a pilot locking plunger 16 and a main lockingplunger 6. The cam 3 can be coupled with and uncoupled from the cam 2 byway of the pilot locking plunger 16 and the main locking plunger 6.

The pilot locking plunger 16 illustrated in FIG. 4 in the de-interlockedposition is mounted so as to be displaceable in a blind-hole bore 17,which is disposed in the region of the base circle 14 of the cam 2,preferably in its edge region, and thus at approximately 90° relative tothe main locking plunger 6. A groove-like guide 8, with which and fromwhich the controllably displaceable pilot locking plunger 16 can beengaged and disengaged, is disposed in the region of the base circle 15of the cam 3 mounted rotatably on the camshaft 1. The groove-like guideextends by approximately 180° in the region of the base circle 15 of thecam 3.

The displacement of the pilot locking plunger 16 in the direction of thegroove-like guide 8 takes place in a manner so as to be regulated, bymeans of oil pressure of the pressurized circulating lubricating-oilsystem of the internal combustion engine. For this purpose, a supplyduct 22, which is in communication with a bore 12 running in thelongitudinal direction of the camshaft 1, opens into the blind-hole bore17. The blind-hole bore 17 is therefore in communication with a controlduct 11 b disposed in a bearing 5 of the camshaft 1, by way of a radialduct branched off from the bore 12. The pressurized-oil supply to thecontrol ducts 11 a and 11 b takes place by way of isolating valves thatcan be regulated, not shown. For this purpose, the connectable anddisconnectable control duct 11 a serves to de-interlock the cam 3, andthe connectable and disconnectable control duct 11 b serves to interlockthe cam 3. A spring 18, which acts against the oil pressure acting todisplace the pilot locking plunger 16 in the direction of thegroove-like guide 8, is disposed at the bottom of the pilot lockingplunger 16.

The main locking plunger 6 illustrated in FIG. 3 in the de-interlockedposition is mounted so as to be displaceable in a blind-hole bore 20disposed in the region of the cam 2. The controlled displacement of themain locking plunger 6 in the direction of the cam 3 takes place bymeans of a spring 7 disposed between the bottom of the main lockingplunger 6 and the bottom of the blind-hole bore 20, and also by means ofthe oil pressure of the pressurized circulating lubricating-oil systemof the internal combustion engine, which pressure can be regulated. Forthis purpose, the blind-hole bore 20 in the region of the cam 2 is incommunication with a control duct 11 b disposed in the bearing 5, by wayof a radial duct 21, an axial duct 12 disposed in the camshaft 1, and afurther radial duct disposed in the camshaft 1.

A blind-hole bore 13, in which a sealing plunger 19 is disposed so as tobe displaceable, is disposed in the region of the cam 3, pointing in thedirection of the cam 2. The blind-hole bore 13 is in communication witha control duct 11 a of the controllable pressurized-oil supply, by wayof a radial bore 10 disposed in the camshaft 1, the axial duct 4disposed in the camshaft 1, and a further radial bore 9 disposed in thecamshaft 1.

The principle of action of the valve drive for internal combustionengines, according to the invention, is the following:

During full-load operation, the cam 3 provided with the larger camprofile is engaged with the gas-exchange valve by way, for example, of acam follower. In the process, the cam 3 mounted rotatably on thecamshaft 1 is connected, by means of shape fit, with the cam 2 disposedon the camshaft 1 so as to rotate with it, as illustrated in FIG. 1. Acorresponding oil pressure bears on the bottom of the pilot lockingplunger 16, by way of the supply duct 22, which pressure has displacedthe pilot locking plunger 16 into the groove-like guide 8 of the cam 3.In an interlocked position of the cam 3 with the cam 2, the pilotlocking plunger 16 bears on the outer boundary of the guide 8, as viewedin the direction of rotation of the camshaft 1. The main locking plunger6 is partly displaced into the blind-hole bore 13 of the cam 3, byvirtue of the oil pressure acting on the main locking plunger 6, so thatshape-fit contact between the cam 3 and the cam 2 exists by way of themain locking plunger 6.

During partial-load operation of the internal combustion engine, with asmall valve lift or a zero lift, the connection between the cam 3 andthe cam 2 is separated. In the process, the oil pressure acting on thepilot locking plunger 16 and on the main locking plunger 6 by way of theradial duct 21 is disconnected by means of a control device, which canbe regulated, so that these plungers are depressurized. The pilotlocking plunger 16 is retracted, by means of the spring 18, into theblind-hole bore 17. At the same time, pressurized oil is admitted to theblind-hole bore 13, by way of the radial bore 10. The oil pressuredisplaces the sealing plunger 19, and thus the main locking plunger 6,until the latter is located completely in the blind-hole bore 20 of thecam 2. The cam 3 is therefore de-interlocked, and the cam 3 is no longerdriven indirectly by the camshaft 1.

If the internal combustion engine is run in full-load operation onceagain, coupling of the cam 3 with the cam 2 takes place once again, as afunction of the engine-specific parameters. Pressurized oil is suppliedto the blind-hole bore 17 by way of a control duct 11 b and the supplyduct 22, and to the blind-hole bore 20 by way of the radial duct 21. Thepilot locking plunger 16 is displaced, by means of the oil pressure, inthe direction of the cam 3, and can be inserted into the groove-likeguide 8. Secure insertion of the pilot locking plunger 16 during theinterlocking operation is achieved by means of the fact that the guide 8extends over approximately 180° in the region of the base circle 15.After the pilot locking plunger 16 has been inserted into the guide 8,the cam 3 is carried along by means of the pilot locking plunger 16.Because of the force of the spring 7 and the oil pressure bearing on themain locking plunger 6, the main locking plunger 6 is displaced partlyinto the blind-hole bore 13 during axial alignment of the blind-holebore 20 and the blind-hole bore 13. In this way, the interlockingprocess is completed and the cam 3 is active on the gas-exchange valve.

LIST OF REFERENCE SYMBOLS USED

-   1 Camshaft-   2 Cam-   3 Cam-   4 Duct-   5 Bearing-   6 Main locking plunger-   7 Spring-   8 Guide-   9 Radial bore-   10 Radial bore-   11 a Control duct, connectable and disconnectable, for    de-interlocking the cam 3-   11 b Control duct, connectable and disconnectable, for interlocking    the cam 3-   11 Bore-   12 Blind-hole bore-   13 Base circle of the cam 2-   14 Base circle of the cam 3-   15 Pilot locking plunger-   16 Blind-hole bore-   17 Spring-   18 Sealing plunger-   19 Blind-hole bore-   20 Radial duct-   21 Supply duct

1: Valve drive assembly for an internal combustion engine, with at leasttwo cams disposed on a camshaft and provided with different profiles,which cams selectively actuate at least one gas-exchange valve, andwherein one cam is connected to the camshaft so as to rotate with it,and the other cam is mounted rotatably on the camshaft and can beconnected, by means of shape fit, to the cam disposed on the camshaft soas to rotate with it, by way of a controllable locking plunger, whereina groove-like guide (8) is disposed in the region of the base circle(15) of the cam (3) mounted rotatably on the camshaft (1), with whichguide a pilot locking plunger (16), which is mounted so as to becontrollably displaced in a blind-hole bore (17) of the base circle (14)of the cam (2) connected to the camshaft (1) so as to rotate with it,can be engaged and from which guide it can be disengaged. 2: Valve driveassembly according to claim 1, wherein the groove-like guide (8) extendsover approximately 180° in the region of the base circle (15) of the cam(3). 3: Valve drive assembly according to claim 1, wherein theblind-hole bore (17) is in communication with a controllablepressurized-oil supply for displacement of the pilot locking plunger(16) in the direction of the groove-like guide (8). 4: Valve driveassembly according to claim 1, wherein a spring (18) is disposed on thebottom of the pilot locking plunger (16), which spring acts against theoil pressure acting to displace the pilot locking plunger (16) in thedirection of the groove-like guide (8), and displaces the pilot lockingplunger (16) in the direction of the bottom of the blind-hole bore (17)upon disconnection of the oil pressure for displacing the pilot lockingplunger (16) in the direction of the groove-like guide (8), and theconnection of the cam (3) with the cam (2) is de-interlocked by means ofthe pilot locking plunger (16). 5: Valve drive assembly according toclaim 1, wherein a blind-hole bore (20) is disposed in the region of thecam (2), in which bore a displaceable main locking plunger (6) iscontrollably mounted, which plunger can be engaged with and disengagedfrom a blind-hole bore (13) disposed in the region of the cam (3). 6:Valve drive assembly according to claim 1, wherein the blind-hole bore(20) in the cam (2) and the blind-hole bore (13) in the cam (3) are incommunication with a controllable pressurized-oil supply fordisplacement of the main locking plunger (6). 7: Valve drive assemblyaccording to claim 1, wherein a spring (7) is disposed between thebottom of the main locking plunger (6) and the bottom of the blind-holebore (20) in the cam (2). 8: Valve drive assembly according to claim 1,wherein a sealing plunger (19) is disposed in the blind-hole bore (13).